The invention relates to sheet feeders and more particularly to sheet feeders for supplying sheets of material such as paper to office copying and printing machines and the like.
Many types of sheet feeders are used in office supply equipment. For example, paper sheet feeders are widely used in copying machines and printers. In such machines, single sheets of paper are taken from a pile of paper, and the single sheets of paper are fed one by one to a photo drum or to a printer. The individual sheets are then correctly positioned. In some machines, mispositioned or misaligned sheets are simultaneously adjusted by using a plunger-type solenoid which shutters the flow of paper to stop the sheets physically at a pre-set point. Such sheet feeding devices are well-known.
Referring to FIG. 4, one example of a conventional sheet feeder used for feeding papers to a photo drum in an electro-photographic copying machine will be explained.
In the embodiment of FIG. 4, 41 denotes a sheet of paper, 42 denotes a paper cassette, and 43 denotes a feed roller. The embodiment of FIG. 4 further comprises transfer rollers 44, 44', 47, 47', and a shutter 45 which pivots by the action of a solenoid plunger 46 about support point 45a in the direction of the rotating arrow shown in FIG. 4. The paper 41 is fed by the feed roller 43 from the cassette 42 along guide plates G and is stopped temporarily by the shutter 45 as the front edge of the paper contacts the shutter 45. The paper 41 is then fed to the photo drum as needed (photo drum not shown).
Under the above conventional configuration, since a solenoid plunger was used, the total cost of the conventional machine, including the solenoid electric circuit, was high. Furthermore, when thin paper was fed, the thin paper was often easily bent and wrinkled by the shutter or the shutter operation. Additionally, when the shutter 45 opened as described above, bent paper could accidentally slip or otherwise be advanced beyond the shutter, and due to this over-slipping or advancement, the paper would be often mispositioned.
It is therefore an object of the invention to eliminate the above-described demerits of conventional sheet feeders and to propose a sheet feeder which is low in cost, secures stable feeding and prevents or corrects mispositioned paper.